1. Field of the Invention
The present invention relates to a time division multiplexing communication system, a time division multiplexing communication switch system, and a communication control method of a communication system for performing a demand assignment time division multiple access (TDMA).
For example, the present invention relates to a time division multiplexing communication system, a time division multiplexing communication switch system, and a communication control method of a communication system which are connected to a communication device via a coaxial cable to control communications between coaxial cables using a transmittal right for the communication device, and share a transmission band.
2. Related Art of the Invention
The time division multiplexing communication system having a communication device for performing the demand assignment TDMA communication and a transmittal right management device for assigning a transmittal right in the conventional technology is explained below by referring to the attached drawings.
The TDMA communication is widely known as a communication system in which a time slot for transmission of information is formed by time-dividing a transmission band, and the time slot is assigned to a communication device for transmitting information. In this communication system, a TDMA frame, which is a fundamental period in a transmission line, is time-divided into a number of time slots, and each communication device uses any of the time slots to transmit information to a corresponding communication device. Then, the corresponding communication device selects a time slot addressed to it, and receives the information.
In the TDMA communications, if a plurality of communication devices simultaneously use the same time slot, a plurality of signals conflict with one another and information cannot be correctly transmitted. Therefore, a time slot being used by any communication device must be prevented from being used by another communication device.
To solve this problem, in the demand assignment TDMA communications, each communication device issues a send request to a transmittal right management device each time information is to be transmitted, the transmittal right management device selects a free slot, and assigns a transmittal right to each communication device (for example, refer to Japanese Patent Application Publication No. 2-183644). Thus, the conflict among a plurality of signals can be avoided.
The entire disclosure of Japanese Patent Application Publication No. 2-183644 is incorporated herein by reference in its entirety.
FIG. 9 is a block diagram of the configuration of the coaxial connection device used in the demand assignment TDMA communication system according to the conventional technology.
A coaxial connection device 71 is provided with a plurality of coaxial terminal units 611 to 61n to which a coaxial cable is connected, and the coaxial terminal units 611 to 61n are all interconnected via an internal connection line 62.
FIG. 10 shows the configuration of the time division multiplexing communication system for performing the demand assignment TDMA communication according to the conventional technology.
The communication system is composed of the coaxial connection device 71, communication devices 721 and 723 to 72n, and a transmittal right control device 73. The communication device 721, the transmittal right control device 73, the communication devices 723 to 72n are connected to the coaxial terminal units 611 to 61n of the coaxial connection device 71 through coaxial transmission lines 741 to 74n. 
FIG. 11 is an explanatory view of the time frame of the communication system shown in FIG. 10.
A time frame is composed of frames of a send request period 81 in which the communication devices 721 and 723 to 72n transmit a transmittal right, a transmittal right notification period 82 in which the transmittal right information assigned by the transmittal right control device 73 is transmitted, and an information transmission period 83 in which the communication devices 721 and 723 to 72n transmit information among the communication devices. The information transmission period with another communication device assigned to one communication device configures one frame, and the information transmission period 83 is composed of a plurality of frames indicating the information transmission period in each communication device. In this example, a frame indicating the information transmission period between the communication device 721 and the communication device 723 assigned to the communication device 721 is defined as an information transmission period 84.
FIG. 12 is an explanatory view of the configuration of the send request information of the communication system shown in FIG. 10.
The send request information is composed of destination information 91 (communication device ID, etc.), source information 92 (communication device ID, etc.).
FIG. 13 is an explanatory view of the assignment information of the communication device shown in FIG. 10.
The assignment information is composed of a combination of a plurality of destination information 101 (communication device ID, etc.) about an assigned transmittal right, source information 102 (communication device ID, etc.) about an assigned transmittal right, and assigned sending period information 103 for each communication device.
Described below are the operations of the coaxial connection device 71, the communication devices 721 and 723 to 72n, and the transmittal right control device 73 performed when information is transmitted from the communication device 721 to the communication device 723 in the communication system shown in FIG. 10.
The communication device 721 generates send request information from the destination information 91 (communication device ID, etc.) about the destination communication device 723 and the source information 92 about the source communication device 721. Then, in the send request period 81, the send request information is transmitted to the transmittal right control device 73 through the coaxial transmission line 741.
The transmission information sent from the communication device 721 is received by the coaxial terminal unit 611 connected to the coaxial transmission line 741 of the coaxial connection device 71. Then, it is transmitted to the coaxial terminal units 612 to 61n connected by the internal connection line 62 of the coaxial connection device 71, and transmitted to the coaxial transmission lines 742 to 74n connected to them.
The transmittal right control device 73 receives the transmission information from each communication device through the coaxial transmission line 742, and extracts send request information from the transmission information received in the send request period 81 shown in FIG. 11. Then, the process of assigning a transmittal right from the destination information 91 (relating to the communication device 723 in this example) and the source information 92 (relating to the communication device 721 in this example) to the communication devices 721 and 723 to 72n (relating to the communication device 721 in this example) is performed.
Then, the transmittal right control device 73 generates from the assigned transmittal right the transmittal right information to the communication devices 721 and 723 to 72n composed of the destination information 101, the source information 102, and the sending period information 103, and transmits the transmittal right information to the communication devices 721 and 723 to 72n through the coaxial transmission lines 741 to 74n in the transmittal right notification period 82.
The transmittal right information transmitted from the transmittal right control device 73 is received by the coaxial terminal unit 612 connected to the coaxial transmission line 742 of the coaxial connection device 71, transmitted to the coaxial terminal units 611 and 613 to 61n connected by the internal connection line 62, and transmitted to the coaxial transmission lines 741 and 743 to 74n connected to them.
The communication device 721 receives the transmittal right information from the coaxial transmission line 741 in the transmittal right notification period 82, and transmits transmission information to the communication device 723 through the coaxial transmission line 741 in the information transmission period 84 between the communication device 721 and the communication device 723 in the information transmission period 83 assigned by the destination information 101, the source information 102, and the sending period information 103.
The communication device 723 receives transmittal right information from the coaxial transmission line 743 in the transmittal right notification period 82, then receives the transmission information from the communication device 721 in the information transmission period 84 between the communication device 721 and the communication device 723 in the information transmission period 83 assigned according to the destination information 101, the source information 102, and the sending period information 103.
Thus, the communication devices 721 and 723 to 72n transmits a transmittal right to the transmittal right control device 73 through the coaxial connection device 71, and information can be transmitted between communication devices by the transmittal right control device 73 assigning a transmittal right at a transmittal right.
However, in the time division multiplexing communication system using the same frequency band, in a time period when communication occurs between a set of communication devices connected to the coaxial connection device 71, other communication devices cannot perform communications in the same time period and are kept waiting. Therefore, efficient transmission cannot be performed.
Therefore, the above situation may result in a delay in the transmission of information, or, for example, when the data requiring the immediacy such as an image data, data transfer may not be performed in a requested time period. Thus, in the worst case, the data to be transmitted in the time period sometimes cannot be transmitted.
The present invention has been developed to solve the above-mentioned problem, and aims at providing a time division multiplexing communication system, a time division multiplexing communication switch system, and a communication control method of a communication system capable of performing communications among a plurality of communication devices in the same time period using the same frequency band, thereby efficient transmitting information.